More particularly, the invention concerns chelating diphosphino ligands especially useful for oxo or hydroformylation processes designed for relatively low pressure operation for the preparation of unusually high proportions of normal or unbranched aldehydes from .alpha.-olefins, particularly n-butyraldehyde from propylene.
The use of the present ligands in the rhodium catalyzed hydroformylation of olefins offers significant advantages over the use of monodentate ligands such as triphenylphosphine in that only small quantities of bidentate ligand are required for obtaining high selectivity to linear aldehyde product. By contrast, high concentrations of costly monodentate triarylphosphine ligands are required in order to obtain similar selectivity thus incurring high capital costs.
The present ligands are compounds of the general formulae ##STR2##
Z, when present, represents the atoms necessary to form with adjacent carbons on the benzene nucleus a fused divalent ring structure having up to about 20 ring carbons, preferably, said fused ring structure being selected from divalent naphthalene, anthracene, phenanthrene, pyrene, perylene, fluorene, quinoxaline, quinoline, isoquinoline, benzothiophene, benzofuran, benzoxazole, benzothiazole, benzimidazole, 5,6-benzoquinoline, 7,8-benzoquinoline, 1,2-benzisoxazole, or 2,1-benzisoxazole;
each ring is unsubstituted or substituted with up to three R substituents selected independently from alkyl, alkoxy, aryloxy, aryl, aralkyl, alkaryl, alkoxyalkyl, cycloaliphatic, halogen, alkanoyl, alkanoyloxy, alkoxycarbonyl, carboxyl or cyano;
each R.sub.1 and R.sub.2 is selected independently from alkyl, aryl, aralkyl, alkaryl or cycloaliphatic;
each A is a carbon atom which is either unsubstituted or substituted with one or two independently selected R substituents;
each of the above hydrocarbon groups or moieties of R, R.sub.1 or R.sub.2 may be substituted with 1-3 of the aforesaid R substituents;
each of the above alkyl groups or moieties is straight or branched chain of 1-20 carbons, preferably 1-8 carbons, each aryl group contains 6-10 ring carbons, and each cycloaliphatic group contains from 4-6 ring carbons; and
each Y is independently selected from the elements N, P, As, Sb and Bi, with P being preferred.
In a particular embodiment of the present invention we have discovered that the above structural arrangements of two phosphorus atoms in that particular spatial arrangement, when coordinated to rhodium carbonyl under hydroformylation conditions promotes the formation of linear aldehyde products to an exceptional degree. This feature allows more efficient use of olefinic feedstocks for the preparation of the desired linear aldehyde products. Thus, the hydroformylation of propylene gives normal butyraldehyde, a precursor for the valuable solvent n-butanol, and 2-ethylhexanol, an ingredient in plasticizers. The hydroformylation of 1-pentene and 1-butene gives precursors of the solvents 1-hexanol and n-amyl alcohol. In the hydroformylation of 1-hexene and 1-octene carried out on a commercial scale, this invention would permit the preparation of heptanal and nonanal with a high selectivity to linear isomers that would lead to the corresponding alcohol and carboxylic acid end products having utility for the preparation of plasticizers, synthetic lubricants, and detergents. The hydroformylation of 1-decene and 1-dodecene would lead ultimately to the preparation of 1-undecanol and 1-hydroxytridecane which are useful as fabric softeners, and as ingredients for plasticizers and detergents.
Likewise, the present ligands would have substantial utility in the promotion of certain other transition metal catalyzed reactions such as in combination with platinum and Group IVA metals such as tin where other chelating disphosphine ligands as disclosed in U.S. Pat. No. 4,229,381 have been employed in the hydroformylation of olefins.
It is within the scope of this invention that substituent groups can be attached to the aromatic side chains on the carbons to which the phosphorus atoms are attached, thereby forming diasteriomeric and enantiomeric ligand mixtures which if resolved into optical isomers by means available in the art, would lead to chiral ligands. Such optically active chelate ligands would have utility in asymmetric hydroformylation reactions and would also have utility in the rhodium catalyzed asymmetric hydrogenation of substituted acrylic acid derivatives useful as drug intermediates for the synthesis of R--(--)-pantolactone (see K. Achiva, et. al., Chem. Lett., 297 (1978) and for the hydrogenation of itaconic acid (see K. Achiva, et. al., Tet. Lett., 1475 (1978). Chirality of these ligands is also obtainable by the use of two different hydrocarbyl groups attached to the tetrahedral phosphorus atoms, such as bis(phenyl-n-butylphosphino) diphosphine chelate ligands, which could also be resolved into optical isomers through means known in the art.
The ligands of this invention also would find utility in the nickel catalyzed cross coupling reactions of Grignard reagents with aryl and vinyl halides, a reaction which has been carried out with similar chelating diphosphine ligands as disclosed by K. Yamamoto, et. al., Tet. Lett. 3 (1974) and M. Kumada, et. al., J. Amer. Chem. Soc., 98, 3718 (1976).
The present hydroformylation process in its broad sense comprises contacting at least one olefin having from 2 to about 20 carbon atoms in a reaction zone at a temperature of from about 20.degree. C. to about 250.degree. C. and a pressure of from about 15 psig to about 800 psig with syn gas (H.sub.2, CO) and a catalyst comprising rhodium in chemical complex with one or more of the above chelating diphosphino ligands for a sufficient period of time to permit reaction of said olefin with said syn gas to form aldehyde product.
The present ligands, in particular, those of Examples 2, 3, 4, 5, 7, 8, 9 and 10 of TABLE I below have special utility as a bidentate ligand modifier for the low pressure rhodium hydroformylation of alpha-olefins to prepare aldehyde products with unusually high ratios of normal to branched isomers in high yield. Such products from propylene include n-butyraldehyde which is used to prepare the commercial solvent n-butanol. The hydroformylation of 1-butene and 1-pentene yield intermediate aldehyde products useful for the preparation of the solvents 1-pentanol and 1-hexanol, respectively. The hydroformylations of 1-hexene and 1-octene yield aldehyde products used to prepare the commercially valuable carboxylic acids, n-heptanoic acid and n-nonanoic acid. These same aldehyde products may be converted into alcohols useful for the preparation of plasticizers, synthetic lubricants, and detergents. Likewise, the hydroformylation of higher olefins such as 1-decene and 1-dodecene yield aldehyde precursors to 1-undecanol and 1-hydroxytridecane useful as fabric softeners and ingredients in plasticizers and detergents. These ligands show improvements in hydroformylation technology in one or more areas such as the production of high normal to iso ratios employing relatively small amounts of ligand, increased conversions in low pressure systems, increased catalytic activity and retention thereof over extended periods, and increased catalyst stability.
As a general statement of the actual chemical composition of the present active catalyst species in the reaction zone, the species preferably comprises rhodium complexed with (a) a ligand defined by either of the above structural formulae in a molar ratio of ligand/Rh of about 1/1, (b) H in an atomic ratio of H/Rh of about 1/1, and (c) carbon monoxide in a molar ratio of CO/Rh of about 2/1.
Of the Group VA elements, phosphorus is the preferred for this invention. Of the "R.sub.1 " and "R.sub.2 " hydrocarbon groups, aryl is preferred for both groups yielding the highest selectivity to linear product aldehydes under low pressure rhodium hydroformylation conditions. High selectivities to linear isomer product are also observed if "R.sub.1 " alone is aryl. Selectivity to linear aldehyde product is generally reduced by attaching alkyl or aryl groups to the carbon atoms directly bound to the phosphorus atom.
There are many synthetic routes available to obtain the present ligands and the following examples illustrate some of the routes available to one skilled in the art. The ortho ethyl toluene composition is readily available synthetically from homophthalic acid, a derivative of indene. The following examples are illustrative of the preparation and use of the present ligands and are not intended to limit the invention in any manner. The table below lists the structures given in the examples, and any name abbreviation thereof.
TABLE I ______________________________________ Ex- am- Abbrevia- ple Structure tion ______________________________________ ##STR3## BMBEB 2 ##STR4## BISHOP 3 ##STR5## BENHOP 4 ##STR6## PBENHOP 5 ##STR7## PBUTHOP 6 ##STR8## BEB 7 ##STR9## DIPEB 8 ##STR10## BENPEB 9 ##STR11## 10 ##STR12## ______________________________________